A virtual reality (VR) system is a system which gives a user an experience as if a virtual space is an actual space, by presenting three-dimensional computer graphics (CG) generated by a computer to a user. Further, in recent years, there have also been developed techniques for presenting information which does not exist in a real world, to the user by compositing the three-dimensional CG with a captured image of a real space. The techniques are referred to as an augmented reality (AR) system and a mixed reality (MR) system.
In an AR system, three-dimensional CG can be superimposed on a physical (real) object. For example, in a game shown in Japanese Patent Laid-Open No. 2000-353248 (U.S. Pat. No. 6,972,734B1), three-dimensional CG such as a sword and weapons is displayed superimposed on a captured image of an interactive operation input device held by a user so as to enable the user to freely operate virtual objects (in this case, the sword and weapons).
In such a system, registration accuracy between the physical object and the virtual object is important in order to give a user a sense of immersion. However, it a takes long time to perform calibration for precisely superimposing the virtual object on the physical object, and a skill suitable for performing the calibration is required.